In a paper mill a continuous strip of paper moving longitudinally at high speed must be transversely cut into individual sheets that must then be piled in individual stacks on pallets or the like. The stacking must be done without interrupting the flow of continuously arriving sheets, so that when a stack is complete it is necessary to get it out of the way and bring a new pallet into place while somehow catching and holding the sheets that arrive during the changeover.
Commonly owned U.S. Pat. No. 5,628,595 describes an apparatus having a downstream end spaced upstream in a horizontal longitudinal transport direction from a stacking station for delivering the sheets continuously one after the other at a predetermined upper level in the direction to the station and a main platform vertically displaceable in the stacking station between an upper position below the upper level and a lower position. An auxiliary platform below the upper level is formed by a plurality of parallel rods horizontally displaceable in the direction between an extended position in the station above the main platform and a retracted position upstream of the main platform. This platform is supported in a frame in each of its corners that has a post provided with a lift cable.
Such an apparatus can be very large, producing a stack some 3 m high and weighing several tons. Thus the upper level at which the sheets are fed in is at least 3 m above the floor. In order that service personnel can work on the equipment, for instance to reset it for different sheet sizes, clear a jam, or just perform regular maintenance, it is therefore standard to provide a service walkway or catwalk that is U-shaped, having a pair of longitudinal portions extending horizontally on either side of the stacking station parallel to the longitudinal feed direction and a transverse portion extending between their downstream ends. To work on the apparatus when it is set up for stacking short sheets, another fixed transverse walkway can be provided between the two downstream posts of the machine frame.
U.S. Pat. No. 4,324,397 describes such a machine where an operator platform is provided immediately downstream of the so-called backboard against which the sheets are projected as they are stacked. This platform can move horizontally with the backboard so that the operator is always ideally positioned to observe the stacking operation. While this system is useful for a person actually operating the machine, it does not provide the desired access for most of the repair and maintenance work that must be performed on the stacker.
German patent document 2,633,897 of E. Webb et al (claiming a British priority of Aug. 5, 1975) describes another such operator station in stacking machine. It also does not serve as a platform from which other maintenance or repair jobs can be done.